Impregnation by implosion



MOISTURE CONTENT OF CHIPS (m Z OF OVENE June 4, 1963 G. F. RUSSELL 3,092,536

IMPREGNATION BY IMPLOSION Filed Nov. 19, 1956 2 Sheets-Sheet 1 RADIO FREQUENCY GENERATOR a dc MOISTURE CONTENT OF CHIPS (IN ZOF' OVEN-DRY WEIGHT OF WOOD) BEFORE IMPREGNATION i l 1 I l I IEO- RELATIONSHIP: MOISTURE CONTENT BEFORE AND AFTER IMPREGNATION BY lMPLOSION AVERAGE OF OCCURRANCES, USING DOUGLAS FIR AND WESTERN HEMLOCK "\APREGNATED WITH WATER OR CHEMICAL. SOLUTION- NoTE= BY DEDUCTING BEGINNING MOIETUHE CONTENT FROM ENDNG [\AOISTURE CONTENT AND ADDING EVAPORATION L ..OSS,THE TOTAL AMOUNT OF IMFPEGNATION 1S DETEHMINED- IM PREGNATIO IMPLOSION DRY WEIGHT OF wooo) AFTER BY I Tll3 3-. GEORGE E BY ATTORNEYS June 4, 1963 G. F. RUSSELL 3,092,536

IMPREGNATION BY IMFLOSION Filed Nov. 19, 1956 2 Sheets-Sheet 2 DIELECTRIC RADIO FREQUENCY GENERATOR INPUT K.w. PER TON (DRY BA5IS) CHIPS I60 I40 I00 60 20 H3 K,VV. 220

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CHIP TEMPERATURE BEFORE DIELECTRIC HEATING COST INPUT POWER AT 3Mll l PER K-W- HOUR TO CREATE VAPOR PRESSURE IN CHIPS INVENTOR GEORGE F. RUSSELL MV- W ATTORNEYS 3,092,536 IMPREGNATION BY IMPLOSION George F. Russell, 711 St. Helens Ave., Tacoma, Wash. Filed Nov. 19, 1956, Ser. No. 623,236 4 Claims. (21. 162-50) This case is a continuation-impart of my application on a Flash-Method of Implosion Impregnation of Cellular Material, Serial No. 596,462, filed July 9, 1956, now abandoned.

Chemical pulp has long been used as a component in the production of paper and other materials. Historically it has been produced by impregnating wood in one form or another (but usually in the form of chips) with chemical solutions of various designations and compositions, the combination then being cooked with heat and under pressure in digesters for long periods of time for the pur pose of separating cellulose fibres from the other natural components of wood such as lignin, sugars, etc. After the so-called process of digesting the mixture, the pulp is removed or blown from the pressure vessels and has usually to be washed, bleached or otherwise treated to result in the chemical pulp commonly known in industry.

Recently so-called semi-chemical pulp and chemigroundwood has come into wide use, for the reason that shorter cooks are required and higher yields per cord of wood result both of which factors have induced great amounts of development work to be devoted to its perfection. The chemi-groundwood process like its new brother, the semi-chemical pulp process has in its proc esses certain parallels with the production of full chemi cal pulpthe use of various designations and compositions of chemical solution employed for the purpose of assisting in producing a :delignization or at least partial breakdown of the components of wood. The key step in all chemical, semi-chemical or chemi-groundwood pulping processes is a means of impregnating the wood with the chemical compound or solution which is a major factor in accomplishment of the end result.

The latest technology in chemical pulping considers the problem most retarding the mastery of continuous process digesting to be that of how to quickly get the cooking chemical distributed completely throughout a wood chip so that chemical reaction can take place uniformly. It is recognized by present authorities that it is an inherent part of the cooking process .to increase the temperature very gradually while the impregnating liquor is penetrating the chip so that little or no cooking takes place until the liquor is thoroughly distribtued and diffused through the chip. Such a process is time consuming, requiring as much as an hour and a half for prime grades of kraft pulp, and considerably longer for sulphites. 1n discussing the limitations on chemical pulping imposed by the problem of impregnation, it has constantly been reiterated in the trade that some new method of accomplishing this penetration quickly is necessary.

To force penetration of the chemical solutions into the wood in sulphite or kraft pulping processes, for example, chips and cooking liquor combined under great pressure and heat in large digesters, is the customary means through which this is accomplished; in the semi-chemical process this is accomplished by similar means but in different kinds of pressure vessels; in the chemi-groundwood proc ess, logs are placed in vessels from which air is first evacuated, then the chemicals are thereafter injected under high pressure with the result that the evacuated spaces in the wood may absorb the chemical solution like a sponge. Each type of pulp has impregnating methods of a slightly different type and generally accomplish their end results with varying degrees of efiiciency, but all have common drawbacks and basic deficiencies, namely: (1) the long periods of time required to force penetration of the im- States Patent 3,092,536 Patented June 4, 1963 pregnant into the wood; (2) the costly equipment, the numerous and costly steps and procedures required to accomplish impregnation which might be considered satisfactory; and (3) the oftentimes non-uniform and incomplete penetration of the impregnating liquor into the fibrous areas or intercellular boundaries sometimes designated as the areas which hold hyd-roscopic moisture.

it is accepted in the present state of the art in one process for example to pre-heat chips before impregnation, but heating chips in an oven before impregnation causes case hardening of the outer surface of the chips and thus tends to prevent penetration. Case hardening of a chip in a chemical pulp process merely tends to amplify the deficiency of the chip which as cut with a knife tends to close the fibers around the free space area of the wood, thus preventing easy access of the penetrating liquor while using the means described in this specification to prepare chips for impregnation relieves case hardening and tends to open the free area spaces which have been closed by the action of the chipper knife on the wood.

Preheating chips as by steaming before impregnation has the deficiency of impregnating the chips with more moisture which re-hydrates rather than chemically imice ,pregnates them. This again amplifies the problem of replacing the moisture contained in the chips with the impregnating liquid containing the chemical for cooking.

Another process for example is to effectuate a vacuum in a digester occupied by chips before injecting liquor thereinto to remove the air which is resident inside of the chips for the purpose of allowing the liquor more quickly to penetrate the voids left by the spaces previously occupied 'by air. In this method above atmospheric pressures are used to force the liquor into the chips and as may well be understood there are dozens of variations of devices used to create a greater rapidity of impregnation.

The use of a mechanical device for breaking down chips and forcing the liquor into the interior portions is common in the semi-chemical process. In the production of high yield chemical pulp for example, sometimes called the rapid cook or rapid cycle,'a period of from a few minutes to over an hour is required to allow a degree of penetration considered as satisfactory prior to the commencement of the cooking cycle. The time and effort therefore consumed in penetrating the liquor into the chips may consume considerably greater periods of time than the cooking of the semi-chemical pulp. The difiiculty of penetrating liquor into the chip in the sulphate or sulphite process are so great that in a normal cure cycle of 8 or 10 hours in a digester, the first one, two or three hours may be consumed by creating a sufiicient penetration of the cooking liquor into the chip itself to prevent overcooking the outer surfaces and under-cooking the interior portions.

Another process which has been developed lately to assure more satisfactory impregnation involves the replacement of the air within the chips with some soluble or condensible gas or vapor prior to liquor impregnation. This is accomplished by subjecting the chips to pressures in an atmosphere of sulfur dioxide (for example), this gas being forced into the innermost interstices of the wood to replace the air. In this process called Va-Pu-rge and described in US. Patent No. 2,640,774, issued June 2, 1953, release of the pressure in the chips allows the escape of the gases and with the many repetitions of this pressure and release, the air will eventually be replaced by the gas-es, which it is contended accelerates the mass penetration of the cooking liquid into the wood. These comparatively recent techniques, sometime called Va- Purge and Va-Press and like processes, have drawbacks as deterrents to instantaneous penetration of the liquid used for cooking the chips.

It is in the area of forcing rapid penetration of water or chemical solutions into wood that the invention I have made may be described as fitting into the chemical pulping of wood. My invention has enabled me to force penetration of the impregnating liquid quicker and deeper and with greater uniformity of penetration than any method currently known in the present state of the art, my method being for all intents and purposes instantaneous in its action and thorough in its action. My invention of a flash method of implosion impregnation is new and use- !ful and possesses novelty and commercial practicability.

The usefulness of my invention is not, however, limited to the chemical pulping of wood, but is applicable to the rapid impregnation of almost any substance to which a like problem may be said to apply. Not only would the new process of impregnation be applicable to penetration into chips of sulphite liquor, but also to similar penetration of wood wastes in shredded or other form into which an adhesive solution might desirably be injected as in the manufacture of many types of composite products from waste wood materials. Not only would the new process I have invented be useful in impregnating sulphate liquor into chips for the manufacture of socalled kraft pulp, but also it is usable in the surface impregnation of large pieces of material such as impregnation of the surfaces of grinding wheels with a chemical substance which would improve the surface wearing qualities of the grinding wheel.

The process may be applied in the case of almost any liquid to almost any solid dielectric material, into which neither should the claims as hereinafter set forth be read in the light of so strict a limitation of use.

Other objects and advantage-s will appear as the specification proceeds, and the novel features will be pointed out in the claims hereunto appended.

Drawings For a better understanding of the invention, reference should be had to the accompanying drawings, forming part of this application in which:

FIGURE 1 is a schematic showing of the step in my process of internally heating the chip by dielectric high frequency heating.

FIGURE 2 is a schematic view of a chip illustrating the second step in the process impregnation by Implosion;

FIGURE 3 is achai't showing a relationship which might be said to exist between the moisture content of chips in percentage of their oven dry weight before dielectric high frequency heating and the moisture content of the chips in percentage of their oven dry weight after impregnation by implosion;

FIGURE 4 is another chart illustrating the possible projected electric power to create RF. internal heating of the chips preparatory to impregnation.

While I have shown only one means of carrying out my method of impregnation by implosion, it should be understood that various changes or modifications may be made within the scope of the annexed claims without departing from the spirit thereof.

Detailed Description In describing my invention and particularly to demonstrate its applicability to industrial use among many such tests ofthe process two specific examples or tests have been carried out by me which willset forth the substantial difference between plain immersion impregnation and the method 1 have invented. I have placed a mixture of a liquid solution such as is used in the paper industry in the production of chemical pulp in a tub or vat. A first sample of wood in the form of pulp chips were immersed in the solution until they absorbed the natural amount they are capable of taking on in an extended period of time such as one or two hours. The chips were weighed and tested for moisture content before and after the immersion and it was found that they absorbed about 15% of their oven dry weight of the solution in addition to their beginning moisture content. In the first test sample the. oven dry weight was one and one-half. pounds having a moisture content of 50% of the oven dry weight of the wood. It was therefore found to absorb less than one-quarter of a pound of the liquid solution.

A second test sample of chips the oven dry weight of which was one and one-half pounds having a moisture content of 50% of the oven dry weight of the Wood was exposed to the internal heating effect of a high frequency alternating current field of force to raise the internal temperature of the chips, not purposefully to reduce the natural. moisture content of the wood, but to reach and internally heat the wood and its moisture content throughout its mass to within the neighborhood of the boiling point of water, and to supply in addition a sufiicient amount of the heat of vaporization to change at least a portion of the moisture in the chips into vapor to create a vapor pressure within the chips themselves which did not exist in the same wood at room temperature, the pressure of the vapor substantially displacing the air contained in the chips. While the chips were thus heated, they were immersed in a liquid solution the same as that employed in the test of the first sample of chips, with the result that an implosion took place in the electronically heated chips immersed in the liquid solution and the chips became immediately impregnated by the solution throughout their thickness, the liquid instantly rushing into the chips as would air rush into the space occupied by a vacuum in a vacuum tube in the event of its implosion. The second test samples of chips impregnated by implosion. were found to have a moisture content as expressed in percentage of the oven dry weight of the wood after impregnation of approximately 130. In the ease of the second test sample of chips some heat of vaporization was supplied during the dielectric heating of the chips which would eliminate some of its natural moisture content. On an assumption that 10% of the oven dry weight of the wood was thus eliminated by vaporization, then the amount of the chemical solution absorbed by the process of impregnation by implosion would equal approximately (i.e., l30+1050) of the oven dry weight of the wood which is something slightly more than 1.30 pounds in the ease of the second test sample; compared to something less than .25 pound in the first sample.

In FIGURE 1, I illustrate by way of example the first step of my method of impregnating pulp chips by implosion. A wood chip (or chips) A is shown between the electrode plates B and B of a condenser. The two electrode plates B and B are electrically connected to a radio frequency generator C. The RF. generator may be of the type shown in Patent No. 2,506,158, issued on May 2, 1950, and pertaining to a single standing wave radio circuit or any other type of RP. circuitry deemed satisfactory.

The wood chipsA are internally heated by the radio frequency field of force that is established between the electrodes or condenser plates. The fact that the illustration of FIGURE 1 shows electrodes B and B on either side of the chips A should not indicate that the disclosures herein contained should be limited to the use of plates or electrodes on either side of the chips or to the mass of chips passing therebetween as in a con tinuous process. As well :as the illustration of FIGURE 1 could be an illustration of a circular tube with an elec-- i so as to include air.

trode configuration arranged therearound so as to give the heating effect desired to a moving mass of chips passing through a carrying means of, for example, a tube of Pyrex glass or other type of low heat absorbing material. As well, also, 'FIGURE 1 may have shown a single charged electrode with its opposing unit considered as ground. Nor should FIGURE 1 limit the process as here described as being usable only in connection with a double ender generator of the type described generally in Patent No. 2,506,158 as above set forth; electronic generators of a single ender variety or any other type of electronic generator which will have the effect of creating a high frequency alternating current field of force through which the chips may pass or to which they may be exposed in the course of their heating, may likewise be employed with equally satisfactory results.

In FIGURE 2 is illustrated schematically a chip immersed in a solution of either water or chemical compound after it has been internally heated as above described by passage through a radio frequency field of force or by exposure thereto. The chips, or other form of cellular material is made of a cellular structure that has areas filled with moisture and other areas are spaced The internal heating effect of the high frequency field of force causes the wood and moisture content of the chip material to 'be raised to approximately the boiling point and if left in the field longer than the time required for this effect to be attained, will supply a desired amount of the heat of vaporization for at least a portion of the moisture contained in the material and create within the chip material a vapor pressure. When the chip material thus heated is immersed in a liquid solution shown in FIGURE 2 the surfaces of the chips will be effectively covered by the solution usually at a lower temperature than the chip material itself and the interior of the chip which Was under vapor pressure will instantly be changed due to the sudden collapse of the vapor pressure by condensation to a state simulating a vacuum as schematically diagramed and illustrated roughly as dotted line A in FIGURE 2 but which lineA represents but one instant during the collapse of the vapor pressure. This phenomenon of pressure collapse is caused of course by the sudden changing of vapor pressure back to moisture. Arrows D indicate the direction of the rapid flow of the impregnating solution into the chip A to fill the space created by the vacuum formed as a result of the condensation of the vapor pressure within the chip. Immediate impregnation of the chip by the solution is the result. Mentioned above is a differential of temperature between the chip itself and the impregnating liquor. This is a most natural phenomenon in that any liquid will possess a temperature of less than the same liquid in vapor pressure form. It is therefore desirable to contemplate an electronically heated mass of cellular material being immersed into a solution of a lower temperature than its own, the degree of differential of temperature affecting and substantially controlling the characteristics of the impregnation to be attained.

As the degree of internal vapor pressure is varied, naturally differing temperature gradients will exist between the chips and the impregnant if the impregnant tem perature is constant. Varying degrees of solution penetration will be found to result from the use of diiferent differentials of temperature as between the internal heat of the chips and the impregnating liquor. The amount and depth of the absorption is therefore controllable by variations of temperature gradient, the strength and liquidity of the solution, the moisture content of the chips and the degree of internal vaporization which may result from different treatments in the high frequency field of force as well as other factors. It should be stated here that no matter how a differential is obtained: (1) whether increasing the temperature of the chip in relation to the .temperature of the solution; (2) whether decreasing the temperature of the solution in relation to the temperature of the chips; or (3) whether increasing the temperature of the chip and simultaneously lowering the temperature of the impregnating solution, all are possibilities equally to be considered as methods intended as disclosed by the description of differentials of temperature between the materials and the impregnating solution.

To summarize: When a wood chip at room temperature and medium moisture content is placed in a liquid solution for a two hour soak and removed, it will be found to have taken on a total of only from 15% to 20% of its oven dry weight of the solution in addition to its beginning moisture content, but when the same type of chip is exposed to the internal heating effect of the high frequency alternating current field of force and vapor pressure is created therewithin, its immersion in the same type of liquid solution will result in absorption up to of its oven dry weight of the liquid solution in addition to its beginning moisture content.

When pulp type softwood chips are green and completely saturated, their moisture content can be as much as 100% to of their oven dry weight depending on species; i.e. contain 100 to 150 pounds of water for each 100 pounds of their bone .dry weight. As the chips lose their moisture content by their exposure to the air, they will tend to seek an equilibrium of about 25% moisture content in a reasonable length of time and retain that moisture content which is called hydroscopically-held or that contained in the cellular walls or fibre spaces for long periods of time. Most of the water easily evaporated is the so-called free water which is held in pockets in the Wood. As the chips lose their natural moisture they also tend to lose certain non-condensible gasses and other chemical components of the natural wood and these escape with the first evaporating moisture. Natural rehydration seems never to restore the wood to its natural ability to contain moisture and consequently when by impregnation or pre-hydrolysis, water or a chemical solution is restored to the wood, it will naturally absorb an amount somewhat less than the natural moisture it might contain as a growing timber unless pressure impregnated.

If we consider 150% a maximum of natural moisture content for lowland West Coast hemlock chips, and the chips contain 50% moisture content at the time of their impregnation, the chips could be expected to absorb as a maximum something less than 100% of their oven dry weight; while if the chips contain 80% moisture content, they could be expected to absorb something less than 70% of their oven dry weight. In order to secure penetration of liquids to equal or possibly exceed this natural maximum potential of liquid content resort has in the past been made to high pressure impregnation; in such event somewhat greater moisture contents may be expected. Employing impregnation by implosion, herein described, higher moisture contents generally result after impregnation. Differing strength concentrations of impregnating liquor may therefore be required for treating chips of differing moisture contents so as toget a desired amount of chemical into the chips to result in a proper cooking. A general rule as to amount of absorption may be adopted for the softwoods and a parallel rule, of course, for chips of other species when impregnated by implosion. This relationship may be illustrated as in the chart of FIGURE 3, for example, but it should be noted as set forth in the illustration that by deducting the beginning moisture content from the ending moisture content of the impregnated chips and adding the vaporization loss, the total amount of the potential absorption is determinable. I have determined by experimentation that implosion impregnated chips placed in a pressure vessel containing the same impregnating solution will absorb very little if any more of the impregnating liquor when subjected to pressures of up to *8 atmospheres for periods of as much as one hour than was originally absorbed through the process of impregnation by implosion. Results of such experimental ap- 7 plication of pressures subsequent to implosion impregnation shows that impregnation by implosion is for all intents and purposes as penetrating and as thorough and its absorption as great as is obtained by processes of impregnation used in the present state of the art, which take substantially longer periods of time to accomplish. Impregnation by implosion is instantaneous.

After high frequency heating, similarly effective impregnation is obtained when a liquid solution is sprayed onto the chips instead of the chips being immersed in the solution, but whether or not it is more convenient to spray a solution onto the chips, or whether or not they are more conveniently immersed should not tend .to limit the scope of disclosures herein set forth of the flash effect of this type of impregnation as any method of applying the liquid to the surface of chips may be described as immersion for purposes of the illustrations in this specification.

The heat of radio frequency energy is more expensive than heat created from steam or other means, but it alone accomplishes an internal heating effect in dielectrics and vaporization pressures impossible of accomplishment by other means, so it is therefore desirable to use as little of the radio frequency heat as possible in preparing chips for impregnation by implosion. For example, were the chips raised from room temperature of 72 to 212 F., it would require raising the mass of wood and its moisture content 140 F. If, on the other hand, the chip and its moisture content had obtained an entering temperature by the application of some other form of heat to say 112 F., it would only be necessary that the radio frequency field of force supply energy sufficient to raise the mass 100 F. In the case of chips entering the high frequency field of force at 112 F., having 45 moisture content, it would require just over 170,000 B.t.u.s (or 50+ kw.) of radio frequency energy to raise the temperature of the 2900 pounds of chips (wood and water) to 212 F. and to supply heat of vaporization to that point which creates vapor pressure inside the chip to do the job desired. If, for example, the moisture content of the chip were 22%%, just over 125,000 B.t.u.s (or 37+ kw.) of radio frequency energy would be required to accomplish the same task. Using a typical cost of 3 mils per kwh., and an RF. generator efiiciency of about 50%, the total cost for electric energy of the first illustration would be 34 per ton while that of the second illustration would be only 24 per ton dry basis of wood.

The chart of FIGURE 4, while not intended to be accurate to the last degree and without exactly estimating the heat of vaporization requirements to cause vapor pressure will illustrate the principle here set forth. Entering the left hand margin at 112 F. (see the dotted line F),'the temperature of the chips before electronic heating, and traveling over to a juncture with the upwardly inclined transverse line G, denoting chips of 45% moisture content, the vertical dotted line H which is intersected at the junction represents at its top the total input power required to elevate these chips to that point which (adding about for heat of vaporization) will produce internal vapor pressure, namely 113 kw., while at the lower extremity of the same dotted line H, is the cost for that amount of power at 3 mils per kwh. or 34. Either of these figures may exceed or be less than the exact requirement of a specific variety of wood but will approximate the results to be expected with Douglas fir, hemlock, spruce, white fir and the general run of western softwoods.

My invention makes practical and possible for the first time production of a chemical or semi-chemical pulp without resort to pressure vessels for impregnation and thus eliminates the necessity of creating and maintaining complicated entrance and exit ports in continuous processes and the heavy bolted batches of gargantuan digesters which are excessively expensive. The expression with out resort to pressures above atmospheric does not means to exclude'elevated pressures through pumps or piping where such elevated pressures are used as a means of transport, chip reduction or conveyance as between steps of the processing but is meant to apply to major stages of processing themselves such as impregnating and digesting.

Many new processes are possible therefore: One simplified process may be described as follows: (1) expose the chips to the high frequency field of force through an R.F. electrode configuration designed for such application; (2) drop the internally heated chips quickly into a vat containing a chemical solution to be employed to impregnate the chips or spray the solution onto the chips; (3) remove the chips from the vat on a draining conveyor, and carry the chips to a (4) continuous type refiner, (5) screen, and (6) bleach (if necessary) and prepare for machine. Another process may be described as follows: 1) exposing the chips to the high frequency field of force through an electrode configuration designed for such application; (2) immerse the internally heated for treating in a manner similar to cooking of chips in any normal chemical pulping operation using a digester; (4) break up the chips by blowing, press or disk refining; (5) screen, and (6) bleach (if necessary) and prepare for machine. By no means are these illustrations intended to limit the numberless processes for producing acceptable grades of pulp after the process of impreghating the Wood nor are the illustrations intended to convey the impression that but one grade of end product may result therefrom, but merely shows how my invention makes substantial improvements in the formerly complicated, long and imperfect systems employed in the various methods of impregnating wood chips with a chemical solution, as well as make possible greater production from currently used digesters.

I claim:

1. The herein described flash method of impregnating material of a cellular structure having a moisture content which comprises: heating the said material with radio frequency heat to cause the moisture content to create a vapor pressure within the material; and in immediately bringing an impregnating solution at a lower temperature than that of the vapor pressure, into contact with the surface of the material; whereby the vapor pressure will be collapsed which will immediately create a vacuum within the material and draw the solution into the material to fill the areas previously occupied by the said vapor pressure and thereby impregnate the material practically instantaneous with the solution, by the effect of implosion.

2. In the process of impregnating a solid dielectric material containing moisture with a liquid dielectric material: the steps of elevating the temperature of the material and the moisture for a period of time and causing at least aportion of the moisture to change into a vapor under pressure within the said solid dielectric material by radio frequency internal heating; and thereupon while the internal vapor pressure is maintained, quickly immersing the said solid dielectric material in the said liquid dielectric material which is at a lower temperature than that of the vapor for condensing the vapor and creating a vacuum within the solid dielectric material, the solid dielectric material thereupon becoming instantly impregnated by the liquid dielectric by implosion.

3. In a method for rapidly impregnating moisture-containing pulp chips with a liquid impregnant by the process of implosion, which comprises the steps of: exposing the said chips to the internal heating effect of a high frequency alternating current field of force for a sufficient period of time and at a suflicient temperature for changing at least a portion of the moisture in the chips to a vapor and therewith substantially displacing the air contained in the said chips; and while the internal vapor pressure is maintained, subsequently immersing the said chips in the last liquid impregnant at a lower temperature than that of the vapor for condensing the vapor and creating a vacuum within the chips and causing the liquid to impregnate the chips.

4. In the impregnation of wood with a liquid impregnant by the effect of implosion, the consecutive steps of: first heating the wood in a high frequency alternating current field of force for a period of time sufficient to change at least a portion of the moisture in the wood into a vapor under pressure; and while the internal vapor pressure is maintained, next in the sequel immersing the heated wood in the liquid impregnant at a lower temperature than that of the vapor to condense the vapor and impregnate the wood with the liquid by implosion.

References Cited in the file of this patent UNITED STATES PATENTS 1,972,608 Uhlrnann Sept. 4, 1934 2,137,779 Olsen Nov. 22, 1938 2,442,183 Stearns May 25, 1948 2,631,109 Gard Mar. 10, 1953 2,689,806 Dalton Sept. 21, 1954 

1. THE HEREIN DESCRIBED FLASH METHODD OF IMPREGNATING MATERIAL OF A CELLULAR STRUCTURE HAVING A MOISTURE CONTENT WHICH COMPRISES: HEATING THE SAID MATERIAL WITH RADIO FREQUENCY HEAT TO CAUSE THE MOISTURE CONTENT TO CREATE A VAPOR PRESSURE WITHIN THE MATERIAL; AND IN IMMEDIATELY BRINGING AN IMPREGNATING SOLUTION AT A LOWER TEMPRATURE THAN THAT OF THE VAPOR PRESSURE, INTO CONTACT WITH THE SURFACE OF THE MATERIAL; WHEREBY THE VAPOR PRESSURE WILL BE COLLAPSED WHICH WILL IMMEDIATELY CREATE A VACUUM WITHIN THE MATERIAL AND DRAW THE SOLUTION INTO THE MATERIAL TO FILL THE AREAS PREVIOUSLY OCCUPIED BY THE SAID VAPOR PRESSURE AND THEREBY IMPREGNATE THE MATERIAL PRACTICALLY INSTANTANEOUS WITH THE SOLUTION, BY THE EFFECT OF IMPLOSION. 